In this revised application we show that Perforin-2 (Mpeg1) deficient mice are unable to clear orogastric infection with Salmonella typhimurium and epicutaneous infection with methicillin resistant Staphylococcus aureus (MRSA). Wild type, Perforin-2 sufficient littermates clear both types of bacteria. These findings support our previous in vitro data that showed that Perforin-2 is essential for clearing intracellular bacterial infections. Perforin-2 is expressed ubiquitously: constitutive or inducible by IFNs in all cells derived from endodermal, ectodermal, neuroectodermal and mesenchymal cells. Our data also suggest that killing of bacteria inside cells is responsible fo the inflammatory response observed in bacterial infections and required for bacterial clearance. Our new data in the dextran sodium sulfate model of inflammatory bowel disease suggest that P-2 is responsible for causing the inflammatory response providing novel insights into the pathogenesis of IBD which may be important for developing treatment options for Crohn's disease. In addition, the role of P-2 for anti-bacterial defense provides opportunities for drug development against antibiotic resistant bacterial infections. In ths application we will pursue work in three specific aims. In the first aim we will study mucosal immunity in P-2 sufficient and P-2 deficient mice to orogastric infection with Salmonela typhimurium and determine the role and molecular mechanisms of the inflammatory response in relation to P-2. In the second specific aim we will study the role of P-2 in the induction of diarrhea in the disease model of dextran sodium sulfate (DSS) and the role of P-2 in the composition of the microbiome. In the third specific aim, the susceptibility of P-2 deficint mice to methicillin resistant Staphylococcus aureus (MRSA) will be investigated and the molecular mechanism of P-2 mediated killing of MRSA in keratinocytes studied.